Abstract:The reaction of lanthanoid metal powders (Ln) with sulfur and cesium azide (CsN 3 ) as a nitrogen source in the presence of lanthanoid tribromides (LnBr 3 ) yields lanthanoid nitride sulfides with the composition Ln 4 N 2 S 3 (Ln = Ce-Nd) when appropriate molar ratios of the starting material are used. Additional cesium bromide (CsBr) as a flux secures quantitative conversion (7 days) at 900 • C in evacuated silica tubes as well as the formation of black single crystals. All compounds crystallize isotypically with the orthorhombic crystal structure of La 4 N 2 S 3 (Pnnm, Z = 2) and their structures were determined from single-crystal X-ray diffraction data (Ce 4 N 2 S 3 : a = 644.31 (4)